I find (to a certain extent) that overdrive and distortion pedals react differently to some guitars and particularly amps. So what works great for a strat/marshall can sound weird with a LP/HRD and odd with a rickenbacker/Vox. To a lesser extent they interact with other pedals in the chain if they exist.
So get along to a well stocked store and try a few to get the flavour of what works for you. It would be nice to support the store with the purchase too rather than slink off to try and beat it online.
Sorry if I can't be more specific, I tend to play on the cleaner to overdriven range myself.
Just to throw this in for what it's worth, but it might be worth looking out for a DopeFX (a UK pedal builder) "Iron Lung" or "Earth Dweller" fuzz - he often has ads running on ebay, though not all the time, and sometimes changes the names. Admittedly I haven't tried either pedal, and I'm just going by the descriptions and demos I've watched. I do have a DopeFX Black Lotus overdrive, which honestly is the nicest-sounding overdrive pedal I've owned, and the wiring inside is beautifully done.
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So get along to a well stocked store and try a few to get the flavour of what works for you. It would be nice to support the store with the purchase too rather than slink off to try and beat it online.
Sorry if I can't be more specific, I tend to play on the cleaner to overdriven range myself.